FINANCIAL HIGHLIGHTS (Details) - USD ($) |
12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2022 |
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Investment Company, Financial Highlights [Roll Forward] | ||||||||||
| NAV at the beginning of the period (in dollars per share) | $ 25.29 | $ 22.35 | $ 23.91 | $ 24.09 | $ 23.53 | $ 22.10 | $ 21.24 | $ 20.85 | $ 19.89 | $ 18.59 |
| Net investment income (in dollars per share) | 3.29 | 2.65 | 2.10 | 2.50 | 2.60 | 2.39 | 2.23 | 2.18 | 2.20 | 2.06 |
| Net realized gain (loss) (in dollars per share) | (0.07) | 0.66 | (1.77) | (0.33) | (0.03) | 0.19 | 0.56 | (0.43) | 0.53 | 0.07 |
| Net unrealized appreciation (depreciation) (in dollars per share) | 0.33 | 1.97 | (0.09) | (0.09) | 0.32 | 0.86 | (0.14) | 0.20 | (0.27) | 0.52 |
| Income tax provision (in dollars per share) | (0.31) | (0.48) | 0.21 | (0.02) | (0.09) | (0.43) | 0.02 | 0.18 | (0.15) | 0 |
| Net increase in net assets resulting from operations (in dollars per share) | 3.24 | 4.80 | 0.45 | 2.06 | 2.80 | 3.01 | 2.67 | 2.13 | 2.31 | 2.65 |
| Dividends paid from net investment income (in dollars per share) | (2.95) | (2.58) | (2.46) | (2.91) | (2.69) | (2.47) | (1.99) | (2.49) | (2.17) | (2.29) |
| Distributions from capital gains (in dollars per share) | 0 | 0 | 0 | 0 | (0.16) | (0.32) | (0.74) | (0.16) | (0.38) | (0.37) |
| Dividends paid (in dollars per share) | (2.95) | (2.58) | (2.46) | (2.91) | (2.85) | (2.79) | (2.73) | (2.65) | (2.55) | (2.66) |
| Impact of the net change in monthly dividends declared prior to the end of the period and paid in the subsequent period (in dollars per share) | (0.01) | (0.01) | 0 | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.02) |
| Accretive effect of stock offerings (issuing shares above NAV per share) (in dollars per share) | 1.17 | 0.58 | 0.41 | 0.55 | 0.47 | 1.07 | 0.76 | 0.74 | 1.07 | 1.13 |
| Accretive effect of DRIP issuance (issuing shares above NAV per share) (in dollars per share) | 0.09 | 0.09 | 0.08 | 0.12 | 0.09 | 0.06 | 0.08 | 0.12 | 0.12 | 0.13 |
| Other (in dollars per share) | 0.03 | 0.06 | (0.04) | 0.01 | 0.06 | 0.09 | 0.09 | 0.06 | 0.02 | 0.07 |
| NAV at the end of the period (in dollars per share) | 26.86 | 25.29 | 22.35 | 23.91 | 24.09 | 23.53 | 22.10 | 21.24 | 20.85 | 19.89 |
| Market value at the end of the period (in dollars per share) | $ 36.95 | $ 44.86 | $ 32.26 | $ 43.11 | $ 33.81 | $ 39.73 | $ 36.77 | $ 29.08 | $ 29.24 | $ 32.69 |
| Shares outstanding at the end of the period (in shares) | 78,506,816 | 70,737,021 | 67,762,032 | 64,252,937 | 61,264,861 | 58,660,680 | 54,354,857 | 50,413,744 | 45,079,150 | 39,852,604 |
| NAV at end of period | $ 2,108,586,000 | $ 1,788,846,000 | $ 1,514,767,000 | $ 1,536,390,000 | $ 1,476,049,000 | $ 1,380,368,000 | $ 1,201,481,000 | $ 1,070,894,000 | $ 939,982,000 | $ 792,533,000 |
| Average NAV | 1,923,134,000 | 1,626,585,000 | 1,436,291,000 | 1,517,615,000 | 1,441,163,000 | 1,287,639,000 | 1,118,567,000 | 1,053,313,000 | 885,568,000 | 706,056,000 |
| Average outstanding debt | $ 1,882,462,000 | $ 1,417,831,000 | $ 1,152,108,000 | $ 1,055,800,000 | $ 947,694,000 | $ 843,993,000 | $ 801,048,000 | $ 759,396,000 | $ 575,524,000 | $ 444,331,000 |
| Investment Company, Ratio To Average Net Assets [Abstract] | ||||||||||
| Ratio of total expenses, including income tax expense, to average NAV | 8.05% | 8.56% | 4.95% | 5.75% | 5.75% | 7.37% | 5.48% | 4.63% | 5.82% | 5.82% |
| Ratio of operating expenses to average NAV | 6.84% | 6.54% | 5.89% | 5.67% | 5.32% | 5.47% | 5.59% | 5.45% | 5.11% | 5.82% |
| Ratio of operating expenses, excluding interest expense, to average NAV | 2.77% | 2.92% | 2.44% | 2.36% | 2.30% | 2.63% | 2.58% | 2.41% | 2.44% | 2.95% |
| Ratio of net investment income to average NAV | 12.76% | 11.23% | 9.60% | 10.37% | 10.87% | 10.51% | 10.35% | 10.15% | 10.79% | 10.68% |
| Portfolio turnover ratio | 16.79% | 29.81% | 18.00% | 18.86% | 29.13% | 38.18% | 24.63% | 25.37% | 35.71% | 36.10% |
| Total investment return | (11.18%) | 48.24% | (19.11%) | 36.86% | (8.25%) | 16.02% | 37.36% | 8.49% | (3.09%) | 16.68% |
| Total return based on change in NAV | 13.51% | 21.84% | 1.91% | 8.78% | 12.19% | 14.20% | 12.97% | 11.11% | 12.71% | 15.06% |
| Affiliated Entity | External Investment Manager | ||||||||||
| Investment Company, Ratio To Average Net Assets [Abstract] | ||||||||||
| Total expenses | $ 13,000,000 | $ 10,300,000 | $ 7,400,000 | $ 6,700,000 | $ 6,800,000 | $ 6,400,000 | $ 5,100,000 | $ 4,300,000 | $ 2,000,000 | $ 0 |